338 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
plentiful in any one part of the sponge than.in another. They measure 
0°023 mm. in length, and 0:008 mm. in breadth in the largest examples. 
There are also present much smaller chelze, which are apparently the young 
forms of the above. All intermediate sizes can be seen. 
(ii.) Sigmata. (Text-fig. 17, B.) 
Like the chelze, the sigmata are not numerous in any part of the sponge, 
but they are somewhat more frequent than the former. They are not very 
regular in shape, showing very considerable variation in the amount of the 
curvature, and also in the abruptness of the curve. They measure 0:035 mm. 
to 0:04 mm. across the curve and from 0-001 mm. to 0:003 mm. in diameter. 
Locality. Suez. 
Distribution. Red Sea. 
ESPERELLA SUEZZA, n. sp. (Text-fig. 18.) 
This new species is represented by several specimens, all more or less damaged, 
owing to their very lax nature. Hach specimen consists of a mass of tissue 
showing only a small portion of the true external surface. Several are 
attached to horny Lamellibranch shells (probably Avicula). In those 
specimens where the external surface can be seen, it appears to be fairly regular 
and to be covered with small, very low, rounded prominences, which are on 
the average 5 mm. in diameter. 
The surface is apparently quite smooth and almost glabrous. 
The oscula and pores could not be made out in most of the specimens, but 
in one case a few small oscula were seen, measuring about 1 mm. in 
diameter. 
The colour in spirit is a dirty dark grey. 
The texture of the sponge is very lax, and the sponge is very easily broken 
into fragments. Nearly always, however, the sponge tears apart vertically. 
No further details of external appearance can be given owing to the 
fragmentary nature of the specimens. 
Skeleton arrangement. 
The main skeleton consists of spicular fibres, which lie very irregularly in 
the sponge. They do not form a reticulation of fibres, but le in sinuous and 
irregular lines throughout the sponge. They also do not seem to be very 
long, but frequently stop short abruptly. The fibres branch frequently, 
sometimes forming a tree-like group of fibres, but the fibres never anastomose 
with each other and some of them are very short. <A few fibres project from 
the surface. 
The number of spicules which go to form any fibre varies enormously, 
especially according to whether the fibre is near the surface or far from it. 
In the former case the fibres may contain only 2 or 3 rows of spicules, and 
